Project Summary: Regulatory Role of Tandem Trp Codons in Chlamydial Persistence Chlamydia is an obligate intracellular bacterial pathogen that causes a range of serious diseases in humans. It is the primary cause of bacterial sexually transmitted infections (STI) and the causative agent of infectious preventable blindness, trachoma. The major concern of chlamydial infections is that they are often asymptomatic and undiagnosed, which can lead to chronic sequelae, such as pelvic inflammatory disease and tubal factor infertility. Consequently, chlamydial diseases remain a significant burden on health care systems around the world. In adapting to obligate intracellular growth, Chlamydia has significantly reduced its genome size and eliminated genes from various pathways as it relies on the host cell for its metabolic needs. Most bacteria respond to amino acid limitation by engaging a stringent response, which is a transcriptional program used to adapt to nutrient-poor conditions. The stringent response has also been directly connected with inducing persister cells in various types of bacteria, which have limited metabolic activity and increased antimicrobial resistance. Chlamydia can become persistent when limited for nutrients such as tryptophan (trp). They are morphologically aberrant, display a dysregulated transcriptome, non-replicating, yet remain viable. Chlamydia lacks the genes necessary to deploy a stringent response, and has very few identified regulatory elements. How it responds to stress is an intriguing question. We hypothesize that during trp limitation the decreased translation of key Chlamydia genes with tandem trp codons triggers a persistent phenotype. The first project goal is to determine how trp limitation impacts the transcriptional regulation by the iron-dependent YtgR repressor. We will use a combination of next-gen RNA sequencing, including ChIP-seq, and targeted transcriptional assays to address this. The second project goal is to determine the mechanism of chlamydial cell division blockage during persistence by focusing on several cell division genes containing tandem trp codons. A combination of genetic approaches and morphological studies will be used to determine this. The third project goal is to monitor host-pathogen interactions, including nutrient acquisition, via cell biological studies. Because several genes associated with host-pathogen interactions contain tandem trp codons, how the inclusion interacts with host pathways and organelles is predicted to be altered by trp starvation; pathways involved in inclusion integrity are maintained whereas those that support chlamydial progression through the developmental cycle are negatively impacted. The proposal aims to mechanistically link trp starvation, regulation of translation by tandem trp codon motifs, and physiological abnormalities linked to persistence. Results will lead to the identification of novel diagnostic and therapeutic targets that may identify and treat asymptomatic chlamydial infections.